Sulfur-modified unsaturated cellulose ether and process of producing the same



-Patented Jan. 14,

SULFUR-MODIFIED UNSATUBATED CELLU- LOSE ETHER AND PROCESS OF PRODUC- INGTHE SAME Maurice L. Ernsberger, Wilmington, Del., assignor to E. I. duPont de Nemours 8; Company, Wilmington, DeL, a corporation of Delawaremodification of cellulose ethers.

object is the provision .of a process for increasing.

No Drawing. Application December 14, 1943, Serial N0. 514,285

This invention relates to cellulose ethers. More particularly it relatesto the vulcanization of unsaturated cellulose ethers and the productsthus obtained.

Cellulose ethers have been widely used in many important applicationssuch as films, fibers, molded articl s and ingredients of lacquersandcoating com ositions. For many applications, properties such a'sresilience and high resistance to solvents, which cellulose ethers donot naturally possess to a great degree, are highly desirable. A varietyof treatments have been proposed to modify cellulose ethers in such away that they will possess these desirable properties. Improvements havebeen obtained in many instances, but they are often accompanied byobjectionable changes such as embrittlement or loss of strength.Furthermore, in many instances the procedures previously proposed haveinvolved technical difiiculties and the use of expensive modifying aents. '1

'I'his'invention has as an object a new class of cellulose derivatives.Another object is the provision of a process for making the same. Afurther object is the provision of a process for the An additional thesolvent resistance, resilience and softening point of cellulose ethers.Other objects will appear hereinafter.

These objects are accomplished by the following characterized byincreased resistance to solvents.

In carrying out the process of this invention in the preferred manner,the unsaturated cellulose.

ether is heated in the presence of 1% to 5% of an organic rubbervulcanization accelerator and 0.5% to 5% sulfur, based on the weight ofthe cellulose ether, at a temperature of 90 to 150 C. for 30 minutes to5 hours. Preferably, cellulose ethers containing 0.05 or moreunsaturated ether .substituents per glucose unit are employed.

Unsaturated cellulose ethers suitable for use in this invention can beprepared by any of the several known processes for the preparation ofcellulose ethers. For example, alkali cellulose can be reacted withunsaturated alkylating agents such as alkenyl halides or sulfates untilthe desired Claims. (Cl. 260-432.)

degree of substitution is obtained. By reaction of alkali cellulose witha properly selected mixalkylating agents. Any organic rubber acceleratorcan be used and either elemental sulfur or a sulfur-liberating compound,such as ammonium polysulfide or dibenzyl tetrasulflde, is operable.

The more detailed practice of the invention is illustrated by thefollowing examples wherein parts given are by weight. There are, ofcourse, many forms of the invention other than these specificembodiments.

Exam ne I crotylcellulose film (0.2 crotyl group per glucose unit) isprepared from the corresponding xanthate in a manner analogous to theprepar'atlon of' regenerated cellulose film from viscose solution. Thecrotylcellulose film is impregnated with an aqueous solution containing3% hexa-.

methyleneimine dithiocarbamate and 1.5% sulfur (as ammoniumpolysulfide), dried at room The resulting film is insoluble in aqueouscupramtemperature, and baked for 4% hours at 155 C.

monium hydroxide even after tumbling for 24 hours. The originalcrotylcellulose film dissolves readily in cuprammonium hydroxide eitherbefore or after heating at. 155 C. for 4 /2 hours in the absence ofhexamethyleneimine dithiocarbamate and sulfur. Regenerated cellulosefilm prepared from the xanthate in the usual manner, remains soluble incuprammonium hydroxide after treatment with the hexamethyleneiminedithiocarbamate and ammonium polysulfide solution and baking in a mannersimilar to that described above.

EXAMPLE II Yarn from crotylcellulose containing 0.21 crotyl group perglucose unit is prepared by spinning a sodium hydroxide solution of thecorresponding xanthate followed by regeneration in a manner analogous tothe preparation of viscose rayon. Skeins of this yarn are treated withan aqueous solution containing 2% hexamethyleneimine dithiocarbamate and5% sulfur (ammonium polysulfide is used as the source of sulfur)centrifuged so that the amount of treating solution retained is equal to1.8 times the weight of the dry yarn, dried at room temperature andbaked for 3 hours at C. The resulting yarn has imapart.

proved resilience, becomes insoluble in cuprammonium hydroxide as aresult of this treatment, and is much less sensitive to aqueous alkalisolutions than the original unvulcanized yarn. Similar results areobtained with yarn containing 0.03

- to 0.4 crotyl group per glucose unit and with treating solutionscontaining from 0.5% to of hexamethyleneimine dithiocarbamate and from0.51% to ,sulfur (as ammoniumpolysulfide). In place ofhexamethyleneimine dithiocarbamate, other water-soluble organic rubberaccelerators such as piperidinium pentamethylenedithiocarbamate can beused.

EXAMPLE III Films of crotylcellulose (2.8 crotyl groups per glucoseunit) are cast from a benzene-methanol (90-10) solution containing 4%zinc dibutyldithiocarbamate and 1.25% sulfur based on thecrotylcellulose. The resulting film is heated for one hour at 100 C. Inaddition to being insoluble in organic solvents. e. g., benzene,

Table I Tensitlg P t Fl streng er ccn exor Film lbs. er elongationnumber sq. n.

Original 800 17 145 Vulcanized 880 58 283 The flex durability values areobtained with a Pfund flexor. In this apparatus a test portion of filminch x 2 inches in dimensions and approximately 0.003 inch thick isclamped by theends in two metal clamps approximately 5 inch One of theseclamps is movable so that it can be pressed up against the other withthe test film between them and with the folded edge of the filmextending approximately 0.05 inch beyond the edge of the clamp. "In thismanner the film is bent through a radius of about 0.025 inch, butpressure from the clamps is not applied directly on the fold. Themovable clamp is pulled back and then pulled up to the fixed clamp againwith the film bent on the opposite side. This flexing in oppositedirections is continued until the film cracks. The number of folds whichthe film requires to be broken is recorded as the flexor number. v

Insoluble products are also obtained when the same crotylcellulose isheated at a temperature in the range of 60 to 130 C. in the presence of0.5% to 5% zinc dibutyldithlocarbamate or some other organic rubberaccelerator such as hexamethyleneimine dithiocarbamate, 2-mercaptothiazgline, mercaptobenzothiazole, or ,zincdiethyldithiocarbarnate and from 0.2% to 10% sulf-ur Insolubleproductsare also obtained by heating the crotylcellulose in the presencevof 0.2% to 10% sulfur in the absence of .anaccelerator. now ever, ata-given temperature'in the range of 80 try-1'75? C. a longer time isrequired for vulcanization and the resulting vulcanizates arenot assatisfactory as those prepared, as described above, in the presence ofan accelerator.

Exmrts IV Films of crotylethylcellulose (0.8 crotyl and 1.6 ethyl groupsper glucose unit) containing 4% zinc dibutyldithiocarbamate and 1.25%sulfur are cast from benzenemethanol (90-10) solution, in which all ofthe ingredients are soluble. Upon heating at 100 C. for one hour, clear,flexible films which are insoluble in benzene result. Im- 10 provedproperties are also obtained when the same crotylethylcellulose isheated at a temperature in the range of 80 to 170 C. in the presence of0.5% to 5% zinc dibutyldithiocarbamate and from 0.5% to 5% sulfur untilthe desired degree of modification is obtained. Other organicsolvent-soluble unsaturated cellulose ethers, for example thosecontaining 1.0 crotyl and 1.4 ethyl groups, 1.3 crotyl and 0.9 ethyl, or1.1 methallyl and 1.8 ethyl groups per glucose unit also becomeinsoluble in organic solvents when heated at 100 C. for two hours in thepresence of 4% zinc dibutyldithiocarbamate and 1.25% sulfur.

EXAMPLE V Methallylcellulose (0.66 methallyl group per glucose unit)fibers, prepared by the heterogeneous etherification of cotton fiberswith methallyl choride in the presence of alkali, is impregnated with anaqueous solution containing 2% hexamethyleneimine dithiocarbamate and10% sulfur as ammonium polysulflde, centrifuged to remove excesssolution, dried at room temperature, and baked at 140 C. for one hour.The resuiting vulcanized fibers are more resilient than the. originalmaterial and insoluble in aqueous, I

cuprammonium hydroxide.

ization of unsaturated cellulose ethers are interdependent so that thedesired result may be obtained'under a wide variety of conditions. Forexample. a high degree of unsaturation, elevated temperatures, andactive accelerators are all conducive to bringing about insolubilizationin a short period of time. The individual variables are discussed below.I .45 Any unsaturated cellulose ether is suitable for use in thisinvention. Preferably the unsaturated cellulose ether contains at least0.05 unsaturated ether substituent per glucose unit. Among the suitableethers may be mentioned crotylethyL cellulose, crotylcellulose,methallylmethylcellulose, allylethylcellulose, crotylbenzylcellulose,ethylbenzylcrotyicellulose, pentadlenylmethylceliulose,hydroxyethylcrotylcellulose, .ethylhexadienylcellulose, etc.

A preferred embodiment of this invention is that in which an organicsolvent-soluble unsaturated cellulose ether is used. The sulfur andrubber accelerators are conveniently incorporated in these unsaturatedcellulose ethers through the 0 use of a common solvent to give productswhich are more readily vulcanized than those prepared from unsaturatedcellulose ethers which are insoluble in organic solvents. In addition,the vulcanizates prepared from organic solvent-soluble products have farmore desirable properties than those prepared from the unsaturatedcellulose ethers which are insoluble in organic solvents.

The unsaturated ether substituents preferably ization throughvulcanization treatments. The tended to be illustrative only. Anymodification organic solvent-soluble unsaturated cellulose or variationtherefrom which conforms to the ether preferably contains at least. oneunsatspirit of the invention is intended to be included urated ethersubstituent per five glucose units. within the scope of the claims.These cellulose ethers are more readilyevulcanized What is claimed is:

than those having a lower degree of unsaturation 1. A sulfur modifiedcrotylcellulose insoluble and yield more solvent-resistant vulcanizates.in aqueous cuprammonium hydroxide solution Any organic rubberacceleratormay be used, and having been prepared by the process ofspecific examples .Qf which include, in addition to claim 11.

those already mentioned, 3,5-dimethylcyclohex- 2. A sulfur modifiedmethallylcellulose insoluanonethioisoxime, tetramethylthiuram disulfide,ble iin aqueous 'cuprammonium hydroxide solupentamethylenethiuramtetrasulfide, etc. ,The tion and having been prepared by the process ofzinc dialkyldithiocarbamates are preferred ace, claim 11. g celeratorssince they are especially eflective in i 3. A sulfur modifiedunsaturated cellulose bringing about insolubilization quickly at a rela-5 etherinsoluble in solvents for the unmodified tively low temperatureto give tough, pliable vulether said ether having been prepared by thecanizates. The sulfur used in the vulcanization process of claim 6.

may be in the form of elemental sulfur or it may 4. A modifiedunsaturated cellulose ether 0 be supplied by a compound which is capableof increased solvent resistance and resilience and liberating sulfurunder the vulcanization condlof elevated softening point obtained byheating tions. Such sulfurv n compounds are for exan unsaturatedcellulose ether to a temperature ample ammonium polysulfide, dibenzyltetrasulof 85 to 140 C. with from 1% to 4% sulfur in fide and certainaccelerators such as pentameththe presence of 2% to 5% of a rubbervulcanizaylenethiuram tetrasulfide, etc. Use of a sulfurtionaccelerator.

liberating compound is very often advantageous, 5. A modifiedunsaturated cellulose ether of inparticularly when the sulfur isintroduced creased solvent resistance and resilienceand of through theuse of a common solvent, since sulfur elevated softening point obtainedby heating an may not be suihciently soluble in the solvent usedunsaturated cellulose ether to a temperature of to dissolve orimpregnate the cellulose ether. 85 to 140 C. with from 1% to 4% sulfur.

In general, excellent results are obtained by 6. Process for increasingthe solvent resistance using between 0.5% and 10% of sulfur based on andresiliency and elevating'the softening point the cellu o e th r nd fr mto 6% y of an unsaturated cellulose ether which comweight of thevulcanization accelerator. Preferprises heating said ether at atemperature above ably two to five per cent of the accelerator and 60 C.with sulfur until th product is substanfrom one to four per cent sulfur,based on'the tially insoluble in solvents for the unmodified,

unsaturated cellulose ether, are used. Tough, ther. o

insoluble vulcanizates are obtained using these '7. Process forincreasing the solvent resistance p p t ns f vu a z n a nts. Thevulcaniand resiliency and elevatin the softening oint zatlon in r ientsn be incorporated into of' an unsaturated cellulose ether containing atcellulose ether by means of a common solvent 40 least one unsaturatedether group per five gluor by impregn in the l l se th r with a coseunits in the ether which comprises heating swelling agent containingthevulcanization insaid ther at a temperature above 60 C. with r dl n It ofurse, also possible to carry sulfur untilthe product is substantiallyinsoluble out the vulcanization by first milling the dry inin 1v ts fothe unmodified ether.

gredients with the cellulose ether and then 8. Process for increasingthe solvent resistance heating. and resiliency and elevating thesoftening point Below C. vulcanization is impracticably of anunsaturated cellulose ether containing at slow. The vulcanizationtemperature should lea t on unsaturated ether group per five glu- D blybe above 80 C. and the preferred cose units in the ether which comprisesheating ran e is between 85 and 140 C., although higher said ether at atemperature above C. with sultompcrflturcs can be e P vi ed hey do notfur and a rubber vulcanization accelerator until ec mp h cellulosecther- At lower n the product is substantially insoluble in solventsatures the vulcanization proceeds slowly and at for the unmodifiedether.

much h h r mp u there i danger of 9. Process for increasing the solventresistance overcuring the Product with a resulting loss of 55 andresiliency and elevating the softening point toughnes The vulcanizationtime. depends of an unsaturated cellulose ether containing at lar ely nthe temperature used and y v y least one unsaturated ether group perfive glufrom five minutes to 48 hours r v n l n r. A cose units in theether which comprises heating good criterion for vulcanization is theinsolubility said eth r at 85 140 C. with sulfur and a of the treatedcellulose ether in a solvent in which so bb vulcanization a l ratoruntil th prodit was Ori inal y Soluble The herein proposed net issubstantially insoluble in solvents for the combination of sulfur and anorganic rubber acnmodified ether.

celerator has been found to be ideally adapted for 10, Process forincreasing t solvent tthe treatment of cellulose ethers because it isance and resiliency and elevating the softening much more effective thansulfur al ne and does oint of an unsaturated cellulose ether containnotbring about the objectionable degradation ing at least one unsaturatedether group per five caused by h agents as Sulfur chl r which glucoseunits in the ether which comprises heatliberate acidic materlals havinga detrimental ing said, ether at to C, with sulfur and effect on thecellulose ethers. Furthermore, vulzinc dialkyldlflflocarbamate until theproduct canization with sulf r an n accelerator yields 70 issubstantially .lnsolublein solvents for the uninsoluble products havinggood aging charactermodified ether,

istics while in contrast unsaturated cellulose 11, Process forincreasing the solvent resistethers insolubilized by previously proposedproance and resiliency and elevating the softening cedures graduallybecome brittle. point ofv an unsaturated cellulose ether contain- Theabove description and examples are in- 76 ing at least one unsaturatedether group per five glucose units in the ether which comprises heatingsaid ether at 85 to 140 C. with from 1% to r 4%, based on the ether, of51111111 and from 2% to 5%, based on the ether, of a. zincdialkyldithiocarbamate. 7

12. Process of claim 11 wherein the ether is a crotylcellulose.

13. Process of claim 11 wherein the ether is av methallylcellulose.

8 1% to 4% of sulfur and 2% to 5% of zinc dibutyldithiocarbamate, bothbased on the ether, until the ether is insoluble in. organic solventsfor the untreated ether.

15. Process which comprises heating at 85 to 140 C. a methallylcellulosehaving at least one methalllyl group per glucose unit of the ether with1% to 4% of sulfur and 2% to 5% of zinc v dibutyldithiocarbamate, bothbased on the ether, 10 -untll the ether 1s insoluble in organic solventsfor the untreated ether.

MAURICE L. EBNSBERGER.

